Loudspeaker diaphragm attaching

Abstract: A loudspeaker includes a diaphragm having a neck with an annular edge (21), a voicecoil former (14) having an annular edge, and a spider (10). The annular edge (21) of the neck and the annular edge of the voicecoil former (14) are connected together in an annular groove structure (11) in fixed relationship to the spider (10).

Description: The invention relates in general to loudspeaker diaphragm attaching and more particularly to an improved joint among diaphragm neck, spider and voice coil former. FR-A-2 668 018 shows a loudspeaker comprising, a diaphragm having a neck with an annular edge which is formed in a mould with a voice coil former having an annular edge moulded into the annular edge of the diaphragm; and, a spider which is secured to the diaphragm adjacent the annular edge. The present invention is characterised in that the annular edge of the neck and the annular edge of the voice coil former are disposed and connected together in an annular groove structure in fixed relationship to the spider. In one specific form of a loudspeaker according to the invention a loudspeaker driver basket has the motor structure located in front of the cone with the spider behind the motor structure resiliently supporting the rear edge of the coil former. The voice coil is located at the front end of the coil former. The neck joint is in a groove in the spider. The dual shear action of the neck joint in the novel cone/coil former/spider configuration increases the buckling load of the coil former. The spider groove provides a large bond area between the cone, former and spider, thus making a stronger neck joint. In addition, the groove aids in confining the bonding adhesive to a localized region which improves manufacturability by preventing the adhesive from flowing out of the desired joint. This invention also helps provide consistent acoustic properties of the manufactured loudspeaker drivers embodying the invention. Generally, the adhesives used to couple the dustcap to conventional loudspeakers have variations in their stiffness, mass and damping characteristics. These variations are difficult to control and therefore result in variations in the frequency response of the loudspeakers. The novel cone/coil former/spider configuration eliminates the need for a dustcap and its associated adhesive joint, yet still prevents the ingress of dust into the motor structure and reduces variations in acoustic properties of manufactured drivers embodying the invention. Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawings in which: Fig. 1 is a mostly exploded view of a loudspeaker; Fig. 2 is a bottom view of a loudspeaker; Fig. 3 is a top view of a loudspeaker; Fig. 4 is a sectional view through section 4-4 of Fig. 3; Fig. 5 is a sectional view through section 5-5 of Fig. 2; Fig. 6 is a sectional view of a loudspeaker neck joint according to an alternative mode of the invention; Fig. 7 is a sectional view of a conventional loudspeaker neck joint; and Figs. 8 and 9 are partial axial sectional diagrammatic views of alternate embodiments of the invention with a groove in the dust cap. With reference now to the drawings and more particularly Figs. 1-4 thereof, there is shown an exemplary embodiment of a loudspeaker according to the invention. Rear basket 24, preferably made from aluminium, has a bottom edge 25 coupled to the outer edge of spider 10. The spider is preferably made from a cotton-polyester blend and has a centrally disposed circular groove 11. Spider 10 extends completely over the opening in rear basket 24, thereby additionally functioning as a dust cap to help prevent debris from entering motor structure 20. The central portion of spider 10, located inside groove 11, can be treated or impregnated with various stiffening agents well known in the art to achieve the traditional range of conventional dust cap properties. A light treatment will allow air to pass through spider 10 and over coil former 14, cooling voice coil 15 and motor structure 20. A stiffer treatment helps produce more acoustic energy at higher frequencies and prevents buckling of the membrane at high pressure loads. Paper or plastic cone 12 has annular foam surround 13 disposed around its outer edge 22. The inner annular edge 21 of the cone neck is bonded with the rear edge of coil former 14, preferably made from aluminium, inside groove 11 with a two-part epoxy adhesive, which is then cured at a high temperature. Voice coil 15 is disposed at the front edge of coil former 14 and is preferably made from copper clad aluminium wire. Tinsel leads 16 are coupled to voice coil 15 and are brought out through slits 40 in cone 12. Motor structure 20 is supported on the inside of front basket 30, which is preferably aluminium, and comprises a rearwardly opening cup-shaped yoke assembly formed with an annular recess 44 for accommodating voice coil 15. A neodymium-iron-boron circular disk magnet 18 is sandwiched between yoke 19 and coin 17 coacting with yoke 19 to define an annular recess 44 and to provide a radial magnetic field between coin 17 and the cylindrical wall of yoke 19. Yoke 19 and coin 17 are preferably made from low-carbon steel. In the final assembly, surround 13 is adhesively bonded between the rearward edge of the front basket and the front edge of the rear basket. As best seen in Figs. 3 and 4 front basket 30 has a circular opening 32 for accommodating yoke 19. Circular lip 43 of yoke 19 is bonded to the edge of circular opening 32. Referring to Fig. 4 the distance between the top 30 of front basket 30 and the bottom 24 of rear basket 24 is less than 18 cm (8 inches). Referring to Fig. 5, there is shown an enlarged sectional view of neck joint 50 along section 5-5 in Fig. 2. Generally, coil former 14 and cone 12 are pre-assembled with horizontal plane 53 of surround 13 perpendicular to axial plane 52 of former 14. Cone 12 and the rear edge of coil former 14 are then bonded to spider 10 in groove 11 with a high-temperature, two-part epoxy 51. The groove 11 assists in centering and maintaining the perpendicularity of coil former 14 with respect to horizontal plane 53 of surround 13. In addition, groove 11 aids in confining bonding adhesive 51 to a localised region which improves manufacturability by preventing the adhesive from flowing out of the desired joint and into motor structure 20 or onto spider 10. A particularly important advantage of groove 11 can be seen by comparing neck joint 50 with a prior art neck joint 250, as shown in Fig. 7. In the prior art neck joint 250 only one surface of coil former 214 contacts one surface of spider 210 and cone 212. The neck joint according to the invention shown in Figs. 5 and 6 has a significantly larger bond area to form a stronger joint. Another advantage of the invention resides in the dual shear action of neck joint 50 increasing the buckling load of coil former 14. During operation of the loudspeaker, the coil former is displaced in the direction shown by arrow 54 in Fig. 5 and arrow 254 in Fig. 7. Prior art neck joint 250 creates a non-columnar, uneven pull on coil former 214. In contrast coil former 14 is always in either pure tension or pure compression, thereby extending the life of the neck joint. This feature is particularly important in woofers where the coil former excursions are quite large and create large stresses at the neck joint. Fig. 6 shows an alternative embodiment of the invention. Instead of the spider extending completely over the opening in the rear basket, spider 110, shown in Fig. 6 has a central circular opening concentric with groove 111 and having a smaller diameter than groove 111. Dust cap 160 covers the circular opening as shown to prevent dust from entering the magnetic gap and allowing the differential air pressure at the yoke to equalize the pressure in front of the cone. Referring to Figs. 8 and 9 there are shown axial sectional diagrammatic views of alternative embodiments of the invention with the annular groove in the dust cap. In Fig. 8 dust cap 331 is formed with annular groove 312 accommodating the upper edges of cone 313 and former 314 secured therein with adhesive 317. Adhesive 316 secures the inside edge of spider 315 to dust cap 331. In Fig. 9 spider 325 is formed with an annular groove 322 that accommodates the upper edges of cone 323 and former 324 with spider 325 secured to the outside edge of dust cap 321.

Claims: A loudspeaker comprising, a diaphragm (12) having a neck with an annular edge; a voice coil former (14) having an annular edge; and, a spider (10); characterised in that the annular edge (21) of the neck and the annular edge of the voice coil former (14) are disposed and connected together in an annular groove structure (11) in fixed relationship to the spider. A loudspeaker in accordance with claim 1, wherein the annular groove structure (11) is integral with the spider (10). A loudspeaker in accordance with claim 1, wherein the annular groove structure (11) comprises a dust cap (160) over the voice coil former (114). A loudspeaker in accordance with claim 1, and further comprising a front basket (30) having a rearward edge surrounding an opening (32) and having an inside region; a motor structure (20), coupled centrally to the inside region of said front basket, having inner and outer walls, and including a magnet (18) for providing a magnetic field between the inner and outer walls; a rear basket (24) having a bottom with a bottom edge (25) surrounding a bottom opening and a front edge surrounding an opening; the voice coil former (14) having front and rear edges and having a central lumen, the voice coil former being constructed to pass between the inner and outer walls of the motor structure (20); a voice coil (15) coupled around said front annular edge of said voice coil former (14); the diaphragm (12) having an outer annular edge coupled between the rearward edge of the front basket (30) and the front edge of the rear basket (24); the spider (10) having an outer edge coupled to the bottom edge of the rear basket (24) and having a front face coupled to the rear edge (21) of said voice coil former (14) and said annular edge of the neck, the spider resiliently supporting the voice coil former and the neck. A loudspeaker in accordance with claim 1, wherein the spider (10) extends over the entire expanse of the bottom opening of the rear basket (24); and the rear edge of the voice coil former (14) and the annular edge (21) of the neck are coupled to the spider at a central groove (11) disposed in the front face of the spider. A loudspeaker in accordance with claim 4, wherein the rear edge of the voice coil former (14) and the annular edge (21) of the neck are coupled to the spider (10) at a central groove (11) disposed in the front face of the spider; and the spider comprises a central opening concentric with the annular groove with a diameter smaller than a diameter of the annular groove; the loudspeaker further comprising a dust cap (160) coupled to the spider and extending over the entire expanse of the central opening. A loudspeaker in accordance with claim 4, wherein the loudspeaker is constructed with a distance of less than 18cm (8 inches) between the top of the front basket (30) and the bottom of the rear basket (24).

Inventors: SCANLAN JAMES M, SCANLAN, JAMES M.
Applicants: BOSE CORP, BOSE CORPORATION
Application year: 1994
Main classification: H04R7
IPC codes: H04R7, H04R9